The present invention relates to a semiconductor memory device, and more particularly to a multi-port semiconductor memory device having a RAM port for randomly accessing memory cells and a SAM port for serially accessing memory cells.
In recent semiconductor memory devices, together with increasing memory capacity, there is a trend toward multifunctionalization wherein the functions of parts of peripheral circuits are incorporated therein. Mass production of one type of devices is therefore changing to small production of various types of devices. Man power resources are not expanded easily, so the period of development is required to be shortened.
As an example of a semiconductor memory device developed as having a multi-function, there is a multi-port semiconductor memory device having a RAM port for randomly accessing memory cells and a SAM port for serially accessing data in units of the row. This device has a register for storing one row data for serial access and means for data transfer between the register and memory cells.
In general, the RAM port operates asynchronously with the SAM port. The data transferring means transfers data between the register and memory cells, stopping the operation of the SAM port. During the data transfer; cycle, an address pointer to the start address for read/write of the SAM port is obtained at the timing when a row address signal is received.
The SAM port selects the register using a serial counter in the memory device. Therefore, if data outputted from the SAM port is erroneous, it is difficult to discriminate between a fault in obtaining the address pointer and a fault in the data itself.